CALIFORNIA ELECTIONS / U.S. SENATE : Feinstein, Huffington Slugging Out Final Rounds : Incumbent launches three new TV ads. Challenger appears before Rush Limbaugh fan club and urges supporters to get out the vote.

As America's most expensive congressional race in history headed into its final weekend, Sen. Dianne Feinstein and Republican challenger Mike Huffington jabbed at each other Saturday while concentrating on making sure their core supporters vote.

Feinstein urged on Democrats in Santa Monica, West Hollywood and Van Nuys. Huffington met with Republican groups in Orange County, San Diego, Palm Springs and Bakersfield.

Feinstein launched a blitz on the state's television screens, broadcasting three new commercials backed with an advertising budget for the final week of more than $1.5 million. Still, Huffington's unprecedented $28-million campaign was expected to continue outspending the incumbent.

"We have got to win this election," Feinstein told her supporters. "I have won and I have lost elections. I have never felt it was so important, that the integrity of the whole process was more at stake, than it is in this election. That a United States Senate seat could be bought by someone who I am convinced cares not one whit about the people or California would be terrible."

Rep. Huffington (R-Santa Barbara) reminded his troops in San Diego how far they have come.

"We were 30 points behind, what they call an unwinnable race," the candidate said. "Now we are in a statistical dead heat and we need for you to get out and vote and to call 10 people you know and get them to vote on Election Day."

In addition to showing that the race is very close, recent polls indicate that Huffington and Feinstein have pounded each other so much that neither can claim to be liked by even half of the state's voters. Political analysts say an unusually large portion of the electorate remains undecided in the Senate race because they are disgusted with both of their choices.

The upshot is that experts believe the winner may well receive less than 50% of the vote, which has happened only twice in the last 60 years of California U.S. Senate races--with Barbara Boxer in 1992 and Alan Cranston in 1986.

As the candidates stumped for votes in the Southland, both campaign headquarters were also furious with activity. Among the developments Saturday:

* Feinstein's three new television commercials included one attacking her opponent, another comparing their records of accomplishment in Washington and a third--only to be shown on cable television channels--that highlights the senator's endorsement by eight newspapers.

One ad attacks Huffington for admitting recently that he violated federal law by employing an illegal immigrant nanny for more than four years.

Feinstein employed a housekeeper from Guatemala for about three years, ending in 1983. The senator has maintained that she did nothing improper because when the woman was hired she showed documents indicating she was in the country legally.

On Friday, officials from the Immigration and Naturalization Service said the housekeeper entered the country legally but her visa only allowed her to work at the Guatemalan Consulate and even that permission expired while she worked for Feinstein.

The senator's campaign has said that Feinstein's case is different from Huffington's employment of an illegal immigrant nanny until last year because a 1986 federal law made such hiring a crime. Huffington has blamed his wife for the hiring decision but conceded that federal immigration and tax laws were broken.

Feinstein has shown records demonstrating that she paid taxes and Social Security on her employee.

* The Republican campaign released a letter Saturday from Sen. Bob Dole (R-Kan.) asking why the INS is not investigating Huffington's charge that a Santa Barbara reporter approached his former nanny and claimed to be a Feinstein campaign operative. The Huffington campaign contends that the reporter, who has denied the allegation, offered the nanny a green card if she would talk about her work at the Huffington household.

* Huffington officials also produced a 1988 letter that appeared to be written by Feinstein as she tried to help her former housekeeper, Anabella Piaz, gain permanent residency in the United States. The campaign said the letter indicates Feinstein knew of her housekeeper's illegal status because it says, "Anabella's immigration status has been somewhat mixed up during the years."

But Feinstein officials said the letter does not contradict what the senator has said all along, that she believed her housekeeper had permission to be in the country when she was hired. On the campaign trail, Feinstein said, "When I hired this person in 1980, she submitted to me documentation which I believed was correct. I have broken no laws. Mr. Huffington has. What he is doing . . . is kind of a last-ditch, desperation effort."